| Coke industry is an important industry in China’s economic development,and coking wastewater contains high concentration of organic contaminants,resulting in a difficult treatment.The treatment of coking wastewater is difficult to break through the increasingly strict environmental protection standards.The normal biochemical treatment technology is unsatisfactory for the treatment of complex phenolic coking wastewater,owing to low toxicity tolerance,unsuitable for impact load and large amount of sludge.Besides the concentrations of recalcitrant organic pollutants(ROPs)in bio-treated coking wastewater(BCW),such as long chain hydrocarbons,PAHs and heterocyclic compound are still high,which can’t meet the requirements of membrane separation and result in a high operation cost.Therefore,to make the effluent stably meet the discharge standard and reduce the operating cost have become the recognized problems in the wastewater treatment industry,we urgently need further study and improvement on the existing wastewater treatment process.The research on a simple technology with low cost and high efficiency is an important developing direction of the coking wastewater.The difficult and costly regeneration process limits its application of adsorption on activated carbon.Materials locally available such as industrial wastes and low quality industrial goods can be utilized as low-cost adsorbents,on the one hand,it can reduce the cost of coking wastewater treatment,on the other hand,it can realize resourceful utilization.In this regard,low-cost lignite activated coke and powder coke have received attention,because it normally presents with relatively higher mechanical strength and can also be disposed harmlessly by blending with coke in the iron ore sintering process.In this study,the pore size distribution and surface chemical properties of coal-based carbon materials were taken as starting point,the relationship between the physical and chemical properties and adsorption efficiency was multi-angle associated,the factors controlling adsorption of recalcitrant organic contaminant and the mechanism were explored.A lignite activated coke(LAC)-assisted activated sludge(AS)process was developed for enhancing biodegradation of phenol,while the effects of LAC on sludge properties and microbial community structure were investigated,and the enhanced biodegradation mechanism was clarified.(1)In the aspect of the characteristics of ROPs in coking wastewater,adsorption of ROPs from bio-treated coking wastewater using three kinds of coal-based carbon material tar-based activated carbon(AC),powder coke(PC),and lignite-based activated coke(LAC)were investigated.The results showed that LAC exerted the best removal of COD(55%)and colority(77%)at 30 g/L,pH=4 and 25oC with contact time of 120 mins,nearly 20%and 80%higher than activated carbon and powder coke at their respective optimum conditions.LAC shows higher adsorption efficiency than AC in spite of its less porous structure and much lower surface area,which may be related to surface chemistry.The lowest adsorption efficiency of the PC was due to its much lower surface area and negligible oxygen-containing functional groups.The results showed that the adsorption followed Freundlich isotherm,indicating a heterogeneous adsorption for these substances.In addition,the adsorption behavior over time was followed the pseudo-second-order kinetic model very well,and the surface diffusion is more important in these processes for LAC.(2)In the aspect of the factors controlling adsorption of recalcitrant organic contaminant and the mechanism,the physical properties and surface chemical properties of LAC and AC were further studied,and the essential factors of effective adsorption were determined.The characterization of physical structure was determined using nitrogen adsorption(BET),the characterization of surface chemical functional groups was determined using Fourier infrared(FTIR),photoelectron spectroscopy(XPS),the generated effect in the process of adsorption and the mechanism were studied.Results show that LAC exhibited superior ROC adsorption efficiency(57.9%),which was apparently higher than that of AC(45.2%),in spite of its lower specific surface area(238.05 m~2/g)and pore volume(0.21 cm~3/g).FTIR and XPS characterization indicated that LAC possessed a distinctive configuration of functional groups,of which the basic oxygenic groups(60%)provided more hydrophobic adsorption sites for ROPs.3D-EEM and GC-MS further confirmed that LAC had stronger affinity with the ROPs in BCW,especially for PAHs and heterocyclic compounds.The characterization of ACs indicated that pore structure had no noticeable effects and the surface chemical structure(functional groups dependent on the carbon skeleton),especially basic oxygenic functional groups is the key factor that influences ROPs adsorption efficiency.π-πdispersion interactions,hydrogen-bonding and donor–acceptor interactions are considered prevailing mechanism for ROPs adsorption.(3)In the aspect of the process and mechanism of enhanced biodegradation of phenol by lignite activated coke(LAC)-assisted activated sludge(AS)process,the feasibility of LAC-assisted AS process was evaluated,the LAC-bioenhancement mechanism in the aspect of biological treatability,sludge properties and microbial characteristic was clarified,a relationship between efficiency and microbiological data is established.The phenol removal rate of LAC/AS was significantly higher by2-3 times,the steady condition and less inhibitory effect can be achieved.LAC can serve as the nucleating agent,LAC/AS facilitated the stable microbial community and the activity of attached microorganisms,leading to a elevated capacities for phenol degradation.Bacterial diversity based on 16S high-throughput pyrosequencing technology indicated bioenhancement safeguarded the bacterial richness and diversity from phenol loading shocks and promoted the growth of microbial degrader like Propionibacteriaceae.Besides,a good settling property facilitated the retention of the biomass,resulting in an enhanced and stable performance.This method offers several advantages such as handling convenience,process stability and capacity to handle shock loads.(4)In the aspect of the effect of phenol shock-stress(from 0 to 200 mg/L)on the LAC/AS process,a better understanding of the effect of phenol shock-stress on biodegradation,sludge properties and microbial community were evaluated,the functional bacteria possibly responsible for the biodegradation of phenol was identified.The result revealed that the performance LAC/AS was not disturbed until phenol shock up to 200 mg/L,while 50 mg/L for standalone AS process.In LAC/AS,the development of the predominance bacterium was improved,it is benefit to the withstanding capacity of high concentration phenol and treatment efficiency.In this paper,the enhanced removal behaviors of ROPs by coal-based carbon materials was studie and a LAC/AS system was constructed.The factors controlling adsorption of ROPs from bio-treated coking wastewater and bioenhancement mechanisms were revealed.This study provides a theoretical basis for the application of coal-based carbon materials in the treatment of coking wastewater,which is of great significance for the efficient and low-cost treatment of coking wastewater. |
PDF Full Text Request